1. Field of the Invention
The present invention relates to marine vessels and, more particularly, to a vessel including spaced apart hulls wherein the space between the hulls contains an energy absorbing composition. More particularly, the present invention relates to such a vessel wherein the energy absorbing composition includes hollow microspheres and macrospheres in a resin matrix.
2. Description of Prior Art
Spillage of petroleum products, hazardous chemicals or other compositions damaging to the environment resulting from marine vessel hull rupture during grounding, stranding, collision or other accidents has become a major problem. The Oil Pollution Act of 1990 requires that all craft entering United States territorial water have double bottoms and double sides to form an inner hull and an outer hull, traditionally termed a double hull construction. In large marine vessels, the space between the two hulls typically is at least about two meters. The volume defined by the inner surface of the inner hull comprises the tank storage portion for housing the product being transported. The double hull design conventionally is orthogonally-stiffened by both transverse web frames and longitudinal girder (or longitudinal “webs”) between the inner and outer hulls to form a stiff grid bottom and shell structure beneath and surrounding the tank storage portion of the vessel. A common arrangement also includes the use of a center line longitudinal bulkhead positioned within the tank storage portion to form port and starboard oil tanks. In addition, it is known to utilize a double hull construction with marine vessels in addition to tankers, such as barges, ferries, cargo ships, submarines or the like. While it is known that double hulls can effectively protect against minor impact forces, it is also known that they are ineffective to withstand strong impact forces. Such strong impact forces cause both the inner and outer hulls to be breached thereby resulting in spillage of material such as oil from the tank portion of the vessel or of water to allow water ingress into the vessel.
It has been proposed to provide strength enhancing and shock absorbing elements between the two hulls of a double hull ship. It also has been proposed to provide a foam material between the two hull to provide improved hull strength. Such arrangements are shown, for example in U.S. Pat. Nos. 3,811,141; 3,831,212; 3,840,296; 3,887,952 and 3,911,190. It has also been proposed to utilize hollow beads between the two hulls, as for example by U.S. Pat. No. 3,124,626. While the use of foam material or hollow beads comprise an improvement over a hollow space between the two hulls to effect absorbance and diffusion of force applied to the outer hull and to reduce force transmission to the inner hull, their use is undesirable since a significant portion of the impact force is transmitted to the inner hull.
It has also been proposed in U.S. Pat. No. 5,353,727 to provide a collision guard to the exterior hull surface of a marine vessel which is formed from a lightweight permanent buoyant material, such as a fire retardant foam, in order to improve resistance against forces applied to the exterior hull. Such modules are undesirable since they are subjected to the normal sea forces to which a vessel is subjected resulting in their detachment from the vessel.
It has been proposed in U.S. Pat. No. 5,277,145 to increase the strength of a transom portion of a boat with syntactic foam formed from a resin containing hollow microspheres, usually made of glass. These microspheres generally have a diameter of between about 0.1 and about 300 microns. Such syntactic foam compositions are undesirable for use between hulls of double hull vessels since they preferentially transmit rather than absorb forces applied to them. This is primarily due to the fact that the microspheres, when embedded within a thermosetting resin, are extremely resistant to impact forces and thus transmit impact force through the composition rather than collapsing up to the point wherein very high impact forces are applied to the syntactic foam.
Modified syntactic foams are disclosed in U.S. Pat. No. 3,622,437, which is incorporated herein by reference, for use as buoyant materials to be positioned in sea environments, for example more than a thousand feet below the surface of the sea. Such modified syntactic foams include relatively large hollow spheres which provide a reduced density for the modified syntactic foam as compared to the unmodified syntactic foam.
Accordingly, it would be desirable to provide a double hull construction for marine vessels which includes an energy absorbing composition positioned between the two hulls. In addition, it would be desirable to provide such a composition which does not significantly adversely affect the buoyancy of the vessel when the composition is positioned between the hulls. Furthermore, it would be desirable to provide such a composition which preferentially absorbs energy when excessive force is applied to it rather than transmitting energy to the inner hull so that the probability of breaching the inner hull is substantially reduced or eliminated. In addition, it would be desirable to provide such a composition which is substantially impermeable to non-solvating liquids when free of fractures. Such a composition would substantially reduce the probability of cargo leakage from tanks of the vessel or water to ingress into the vessel even when the vessel's exterior hull is breached with excessive force which normally leads to breaching of the inner hull.